Kinetics of Heterogeneous Reaction of Sulfur Dioxide on Authentic Mineral Dust: Effects of Relative Humidity and Hydrogen Peroxide

Heterogeneous reaction of SO₂ on mineral dust seems to be an important sink for SO₂. However, kinetic data about this reaction on authentic mineral dust are scarce and are mainly limited to low relative humidity (RH) conditions. In addition, little is known about the role of hydrogen peroxide (H₂O₂) in this reaction. Here, we investigated the uptake kinetics of SO₂ on three authentic mineral dusts (i.e., Asian mineral dust (AMD), Tengger desert dust (TDD), and Arizona test dust (ATD)) in the absence and presence of H₂O₂ at different RHs using a filter-based flow reactor, and applied a parameter (effectiveness factor) to the estimation of the effective surface area of particles for the calculation of the corrected uptake coefficient (γ_<i>c</i>). We found that with increasing RH, the γ_<i>c</i> decreases on AMD particles, but increases on ATD and TDD particles. This discrepancy is probably due to the different mineralogy compositions and aging extents of these dust samples. Furthermore, the presence of H₂O₂ can promote the uptake of SO₂ on mineral dust at different RHs. The probable explanations are that H₂O₂ rapidly reacts with SO₂ on mineral dust in the presence of adsorbed water, and OH radicals, which can be produced from the heterogeneous decomposition of H₂O₂ on the mineral dust, immediately react with adsorbed SO₂ as well. Our results suggest that the removal of SO₂ via the heterogeneous reaction on mineral dust is an important sink for SO₂ and has the potential to alter the physicochemical properties (e.g., ice nucleation ability) of mineral dust particles in the atmosphere